THE EFFICACY OF INFLUENZA VACCINE IN ELDERLY PERSONS - A METAANALYSISAND REVIEW OF THE LITERATURE

Objective: To quantify the protective efficacy of influenza vaccine in elderly persons. Data Sources: A MEDLINE search was done using the in dex terms influenza vaccine, vaccine efficacy, elderly, mortality, hos pitalized, and pneumonia. Appropriate references in the initially sele cted articles were also reviewed. Study Selection: Only cohort observa tional studies with mortality assessment were included in the metaanal ysis. In addition, 3 recent case-control studies, 2 cost-effectiveness studies, and 1 randomized, double-blind, placebo-controlled trial wer e reviewed. Data Extraction: Vaccine and epidemic virus strains, age a nd sex of patients, severity of illness, patient status, and study des ign were recorded. Upper respiratory illness, hospitalization, pneumon ia, and mortality were used as outcome measures. Data Synthesis: In a meta-analysis of 20 cohort studies, the pooled estimates of vaccine ef ficacy (1 odds ratio) were 56% (95% CI, 39% to 68%) for preventing res piratory illness, 53% (CI, 35% to 66%) for preventing pneumonia, 50% ( CI, 28% to 65%) for preventing hospitalization, and 68% (CI, 56% to 76 %) for preventing death. Vaccine efficacy in the case-control studies ranged from 32% to 45% for preventing hospitalization for pneumonia, f rom 31% to 65% for preventing hospital deaths from pneumonia and influ enza, from 43% to 50% for preventing hospital deaths from all respirat ory conditions, and from 27% to 30% for preventing deaths from all cau ses. The randomized, double-blind, placebo-controlled trial showed a 5 0% or greater reduction in influenza-related illness. Recent cost-effe ctiveness studies confirm the efficacy of influenza vaccine in reducin g influenza-related morbidity and mortality and show that vaccine prov ides important cost savings per year per vaccinated person. Conclusion : Despite the paucity of randomized trials, many studies confirm that influenza vaccine reduces the risks for pneumonia, hospitalization, an d death in elderly persons during an influenza epidemic if the vaccine strain is identical or similar to the epidemic strain. Influenza immu nization is an indispensable part of the care of persons 65 years of a ge and older. Annual vaccine administration requires the attention of all physicians and public health organizations.